This application is related to and claims priority from Japanese Application No. 2002-114113, filed Apr. 17, 2002.
The present invention relates to an image display apparatus such as a liquid crystal projection apparatus, a reflection type image display projection apparatus or a projection type display apparatus for projecting an image on the screen using an image display device such as a transmission type liquid crystal panel or a reflection type image display device as a light bulb, or in particular to a technique whereby the light from a light source is separated into color light components of predetermined wavelength bands and radiated periodically on an image display device. In this way, the light from the light source of an image display apparatus for projecting an optical image corresponding to an image signal in enlarged form is separated into color light components of predetermined wavelength bands and radiated on the image display device.
In the image display apparatus, an image display device is required for each color because a color image is obtained by projecting the image for each of the colors including red, green and blue, for example, having predetermined wavelengths at a single point. In view of the fact that the image display device is expensive on the one hand and the need of saving energy on the other hand, however, a method has been employed in which images of a plurality of colors are displayed with a single image display device.
The conventional image display apparatus comprising a single image display device will be explained with reference to FIG. 7.
FIG. 7 is a schematic diagram for explaining the configuration of the essential parts of the conventional image display apparatus. In the image display apparatus shown in FIG. 7, the light emitted from a light source 2 of a lamp such as a high-pressure mercury lamp included in a light source unit 1 is reflected from a condensing reflector 3 and enters a cross prism 22 for color separation. The cross prism 22 includes reflection films crossed so as to reflect two types of light, and separates the light into the three color light components of red, green and blue by reflection and transmission.
Each color light component thus separated enters into optical axis moving units 4B, 4G, 4R for moving the optical axis in substantially parallel directions, and makes up the light components 24, 25, 26 with the optical axes thereof repeatedly moved in substantially parallel directions. The optical axis moving units are implemented by moving reflectors in parallel or by rotating a parallelepiped and causing the light to enter into it in the direction perpendicular to the rotational axis thereby to displace the optical axis horizontally with parallel flat plates.
The light components 24, 25, 26 with the optical axes thereof repeatedly moved substantially in parallel enter the reflectors 23B, 23G, 23R arranged in obliquely spaced relation with each other for reflecting each color component selectively. The light components of the three colors are sequentially synthesized and radiated on the image display device. In the process, the positions of the three color light components are controlled individually by the optical axis moving units in order to prevent the color light components from radiating the same position of the image display device 6 at the same time and to prevent the color components from being mixed with each other.
Each light component thus radiated is modulated by the image of the particular color, and the modulated image light component of each color is projected in enlarged form on a screen 8 through a projection lens 7 thereby to produce a color image.
The conventional image display apparatus having the configuration described above poses the problem that in spite of the need of a single image display device, the optical axis moving unit is required for each color. Therefore, the apparatus is bulky, and it is difficult to obtain a compact and inexpensive apparatus.
The object of this invention is to provide a compact image display apparatus by obviating this problem.
In order to achieve the object described above, according to this invention, there is provided an image display apparatus for separating the light from a light source into color light components of predetermined wavelength bands and radiating them periodically on an image display device thereby to project an optical image corresponding to an image signal in enlarged form, the apparatus comprising an optical axis moving unit for moving the direction of the light from the light source periodically at a predetermined rate substantially in parallel and a light separating unit for separating the light from the optical axis moving unit into color light components of a plurality of predetermined wavelength bands, wherein the color light components emitted from the light separating unit are radiated on the image display device thereby to project an optical image corresponding to the image signal in enlarged form.
In the image display apparatus according to this invention, the direction of the light proceeding from the light source is moved periodically in parallel by the optical axis moving unit, after which the light is separated into a plurality of color light components having predetermined wavelength bands and radiated on the image display device. As a result, a fewer number of optical axis moving units are used, thereby making it possible to produce a compact image display apparatus.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.